Shaft seals



Sept. 30, 1958 c. A. STEPHENS ET AL 2,854,267

SHAFT SEALS Filed Oct. 12, 1955 mm ,44 v

llli! mmlkk r States Patent SHAFT SEALS Clifford A. Stephens, Palo Alto,and Robert W.

McCandless, Redwood City,

Application October 12, 1955, Serial No. 540,104 3 tllaims. (Cl. 288-4This invention relates to sealing devices, and more particularly toshaft and rod seals of the type employing leather as the pliant sealingmaterial interposed between the relatively moving elements. It alsorelates to a novel composition of matter used to coat the leatherelement in shaft and rod seals. This application is acontinuationin-part of our application, Serial Number 519,862, filedJuly 5, 1955.

Leather has long been favoredas far superior to most materials as apliant sealing element for shafts, reciprocating rods and the like.Despite this, it is recognized that leather has certain disadvantagesand fails to exhibit, to the degree desired, all the characteristicsneeded to meet the ever increasing requirements for a satisfactory seal.For example, leather varies widely in density, resilience, porosity andflexibility, all of which affect performance and suitability for use assealing elements. Accordingly, over the years much effort has beendirected toward improved processing procedures in an endeavor to providea product of more uniform properties and longer service life. Inaddition, these attempts have included the augmentation of existingproperties as well as the inclusion of new ones.

Another facet of the problem derives from the fact that certain desiredproperties of leather are customarily found only in combination withundesirable ones. For example, a leather having the desired flexibilityis too soft to maintain good sealing contact with an eccentricallyrotating shaft, or one which vibrates or whips as it rotates. Also, aflexible leather usually is quite porous. In consequence, it has a highreservoir capacity for lubricant, an advantageous quality. But thisporosity is also attended by seepage of lubricant through the side wallsof the leather, a highly undesirable quality. Previous elforts to sealthe pores have destroyed the leathers capacity for storing lubricant andhave stiffened the leather objectionably.

The primary object of the present invention is the provision of a sealutilizing as the sealing element specially processed leather in whichthe desirable properties of leather are retained and augmented whileother new properties are added.

Another object is the provision of a sealing element having a main bodyof leather with a coating bonded to at least one surface and serving toseal that surface against loss of lubricant by seepage to reduce greatlythe surface friction, to increase the wearing qualities, and to add tothe mechanical strength of the leather but changing its stiffness onlyto a minimum degree.

Still another object is the provision of a metal-encased shaft sealhaving a flexible leather sealing element that is coated with aresilient covering confined to the surface area of the leather andeffective to prevent seepage of oil through the side wall withoutinterfering with the flow and storage of oil within the body of theleather.

Yet another important object is the provision of a shaft seal having aleather sealing element specially treated on its shaft-contactingsurface with a low-friction coating resistant to attack by lubricantsand having long wearing qualities, whereby the torque loss caused by theseal is reduced to a minimum and the service life is increased.

A further object is the provision of a technique for coating leatherwith a veneer of elastomer applied as a liquid and allowed to dry beforethe application of heat and pressure vulcanize the coating to thesurface area of the leather.

Still another object is a mode of vulcanizing and molding a ring areaonly of a plaque of leather, whereby the unvulcanized center may betrimmed away and subsequently Vulcanized and molded in a difierent sizeand shape.

Yet another object is the provision of novel coating compositionssuitable for sealing the surface of leather, textiles and the like andof imparting new and unique properties thereto in a simple, inexpensiveand highly efiicient manner.

A further object is the provision of a leather sealing element with afilm veneer which is soft, pliant, resilient, abrasion-resistant, whichexhibits a much lower coeflicient of friction than the leather, andwhich does not sculf, ball up, blister or slufi ofi.

Numerous other objects and advantages of the invention will becomereadily apparent from the following detailed specification taken inconnection with the accompanying drawings illustrating typical modes ofpracticing the invention, and wherein:

Figure 1 is a sectional view through a shaft seal in its installedposition and featuring a leather sealing member provided with alow-friction protective veneer on its outer surface only;

Figure 2 is a fragmentary enlarged view through a similar seal buthaving a protective veneer on both of its surfaces;

Figure 3 is a fragmentary sectional view on a further enlarged scale,taken through the sealing member of Figure 2 and showing the thicknessof the coatings on an exaggerated scale for illustrative purposes only;

Figure 4 is a sectional view through a mold used in molding the leatherand vulcanizing the elastomeric surface veneer;

Figure 5 is a fragmentary view of the mold on an enlarged scale showingthe mold closed against a plaque of leather; and

Figure 6 is an isometric view, partly in section, of the leather as itappears after removal from the mold.

Referring to Figure 1, it will be seen that the present invention may bepracticed by incorporating our unique leather sealing element in a shaftseal of any suitable construction, such as the seal generally designated10. The radial flange 11 of a specially prepared leather sealing elementis clamped between a metal washer 12 and the radial flange of a cuppedouter case 13, by means of a cup-shaped inner case 14. Thus, thein-turned edge 15 of the casing 14 is held pressed against the washer 12by the curled-in rim 16 of the outer case 13. The exterior formed inthe" bore wall.

cylindrical surface 17 of the outer case is accurately finished so as tohave a snug press-fit with the side wall of a mounting bore 18 of ashaft housing 19. Seated I against the shouldered inner end 20 of thebore 18 is a suitable hearing, such as an anti-friction bearingindicated at 21. This bearing may be held seated in the bore, as;

by a split spring keeper ring 22, which seats in agroove The bearing'Zllserves to support a shaft 23centra1ly of the mounting'bore 18.

The flexible sealing member interposed between the shaft 23 and the sealcasing is formed principally of leather and is, molded to provide anouter, radially extending, mounting flange 11 and a frusto-conical,axially extending, lip'flange 24. This general shape and form of leathersealing lip is conventional and'has been in common use for many years.The smallest diameter portion of its-inner edge 25 may be held insealingcontact with the shaft 23 by a garter spring 26. V One of the'uniquefeatures of the sealing element is theprovision of a thin film or veneer27 of a special elastomer bonded to the inner or shaft-contactingsurface of the seal. If only one surface of the sealing member Thesesubstances, compounded along with a suitable solvent vehicle in a mannerto be disclosed below, are applied in liquid form to the surface of theleather sealing member and then vulcanized.

' The elastomer does not penetrate beyond the base of the hair poreopenings or of the surface crevices and other imperfections of theleather. This confinement of the veneer to the immediate surface area ofthe leather and its absence from the many voids in the body of the,

leather is highly important and has several advantages.

Thus, the absence of elastomer from the interior 'body of the leatherpermits of a free and natural capillary flow of lubricant within theleather in a path generally parallel to the inner and outer surfaces.Secondly, the many voids naturally presentin the leather are availableas lubricant storage reservoirs. And, thirdly, the inherent flexibilityof the body of the leather is not adversely affected by the presence ofincompressible particles filling' the voids And, of specialsignificance,'the exterior surface of the leather ,or the one in contactwith the rotating shaft 23 is sealed by a thin film of resilientmaterial which is'highly resistant to attack by lubricants, relativelyimpervious to both liquids and gases, and has a-coeificient of frictionat least 50% lower thanthe identical leather sealing element without thesurface coating of this invention.

A second embodiment of the invention is illustrated in-Figure 2 anddiffers from the Figure 1 design in that both sides of the leathersealing element have a surface veneer of elastomer. Thesame referencecharacters have been used as in the first'form'but are distinguishableby the use of a prime. The inner or flesh side of the sealing element isshown coated with a film of elastomer 28' corresponding to the coating27' on the outer or hair side. The film thicknesses are somewhatexaggerated in the drawing since, in practice, a film thickness of 2 tomils has been found most elfective, Greater thicknesses can be employedbut have a tendency to stiffen the leather objectionably and are notfound to add to the service life of the sealing element to any materialextent.

Coating both sides of the sealing element has certain advantages. Itstiflens each side of the leather in equal degree; it provides a smoothfinished surface on both sides of the sealing element; and it provides asubstantially sealed reservoir for lubricant within the body of leatherproper. The outer rim of this reservoir is sealed by the surroundinghousing for the sealing element, leaving only the inner peripheral edgeexposed to the interior of the appliance housing and the supply of oiltherein. If the seal is to be used in a location not exposed tolubricating mediums, then the sealing element canbe saturated withlubricant before installation. Thus, in either mode of use, the sealinedge of the lip has'a continuous supply of oil available at all times.As soon as a film of' oil between the shaft and the contacting edge ofthe seal tends to disappear, it is immediately replenished from thesupply stored by capillary action in the body of the seal. Furthermore,the low'friction coating in direct contact with the shaft contains a drylubricant locked within the coating. This dry lubricant supplements theliquid lubricant within the body of the sealing element.

The coating compositions which we have found to be so satisfactory forsurface films or coatings 27,27 and 28 are'elastomers or rubber-likesynthetics incorporating one or more dry lubricants that are dispersedtherein to impart lubricity and other related properties important to aproperly functioning seal. For example, the coating elastomer may beNeoprene GN or Neoprene GRT, stand ard elastomeric polymer ofchloroprene commercially available from E. I. du Pont de Nemours '& Co.One hundred parts of this material should be compounded for rapid curingand mixed with between 10 and 60 parts by volume of a filling agenthaving lubricating properties such as graphite, molybdenum disulfide,mica or talc. (For graphite, the range by weight is between 20 and 120parts perlOO'parts elastomer.) This mixture is dissolved in a suitablesolvent to provide a low viscosity solution of 520%' solids. If a lowersolids content is employed,

the film does not distribute uniformly to provide a reliably continuousveneer, while a solution of higher solids content is too viscous forsatisfactory results. It will, of

course, be understoodby those skilled in the handling of elastomericcompositions that suitable curing agents, antioxidants and acceleratorsarerequired as usual.

Suitable solvents include a mixture of one or more.

aromatics (toluene, benzene, or xylene and homologues of them)with'paraifin hydrocarbons (e. g., gasoline or kerosene) or ketones(acetone, methyl-ethyl-ketone, and other liquids of the group) ornaphthas. Wide variations of quantities can be used, and which solventmixture is selected will depend on factors such as evaporation ratedesired, cost, toxicity, etc.

"The following specific examples suflice to illustrate the relativeproportions of constituents which have been found particularly suitablein artual practice:

EXAMPLE 1 V Neoprene rubber weight Another composition giving excellentresults employs copolymers of butyl acrylate and acrylonitrile or ethylacrylate and chloro-ethyl-vinyl ether in lieu of neoprene. Such acomposition may be compounded as follows EXAMPLE 2 Polyacrylic elastomerConstituents: Parts by weight Lactoprene BA 12.5 (an acrylonitrile(87.5%

butyl acrylate (12.5%) copolymer) 100 Stearic acid 1 Sulfur 1Triethylene tetramine 4 Graphite 80 Total solids 186 Methyl-ethyl-ketone1504 Toluene 170 Total liquids 1674 Grand total 1860 A third compositionmakes use of nitrile elastomer instead of neoprene. The following is anexample of components by weight found in practice to give excellentresults:

EXAMPLE 3 Nitrile elastomer Constituents: Parts by weight Nitrileelastomer 100 Sulfur 2 Stearic acid 2 Zinc oxide 5Phenyl-alpha-naphthylamine 2 Tetramethyl thiuram disulfide 0.5 Graphite70 Total solids 181.5

Methyl-ethyl-ketone 1470 Toluene 164 Total liquids 1634 Grand total1815.5

Still another composition which we have found to provide an excellentadherent veneer for leather employs chlorosulphonated polyethylene as aprincipal elastomeric 1 Kenflex BKenrich Corp.

In any of these four examples, mica, talc, and molybdenurn disulfide maybe substituted for graphite, in equal volumes. Graphite is, however,preferred.

Any of the foregoing compositions may be applied to.

the leather by dipping, dripping, spraying or other common coatingtechniques. However, since the deposition of a layer of the desiredthickness and uniformity requires contact with the liquid over anappreciable period of time, the dipping and dripping-spraying techniquesare particularly advantageous. Dipping is only practical when it isdesired to coat both surfaces of the leather, while spraying may be usedto coat either one or both surfaces.

The dipping process may be carried out by immersing the leather into atank of the composition while the latter is agitated to keep the solidconstituents in suspension. Immersion should be continued for a periodof 10 to 60 minutes depending upon the thickness of coating'desired. Theleather is then removed and allowed to drain and dry at room temperaturefor a period of 6 to 24 hours after which it is ready for curing andmolding to the desired shape.

The spray coating and dripping procedures will be obvious from theforegoing discussion of the dipping method. A spray, stream, or drippingof the coating liquid is applied to the leather for a period of 10 to 60minutes. Care is, of course, exercised to distribute the coatingcomposition evenly. lf a coating is desired on only one surface, thespray or stream is directed in such a manner as to exclude it from oneside, and it may be dripped only on the upper surface. A preferredmethod is to carry a series of leather blanks or plaques along aconveyor, floating them on a film of the coating composition and passingthem below a series of dripping stations, each of which may comprise ahorizontal bar upon which the coating composition is being sprayed, sothat it drips over the edges onto the blanks passing below. During theperiod of exposure, the flow of composition is discontinued and thepieces are allowed to dry preparatory to curing and molding which may becarried out by the aid of a mold of the type illustrated in Figures 4and 6.

Figure 4 shows a 2-part mold closed against a plaque 40 of coatedleather. The mold includes a lower female member 41 secured to a heatedplaten 42 of a molding press by means of a cap screw 43. The cooperatingmale mold member 44 is similarly secured to an upper platen 45 by a capscrew 46. It will be observed that each of the mold members has a largearea cavity 47, 47 which does not contact the central portion 48 of theleather plaque. The outer opposed surface areas of the mold members 41and 44 have complemental surfaces uniformly spaced from one another andshaped to form a sealing element of L-shape in section as clearlyindicated in the several figures of the drawing.

The narrow radial surfaces 49 and 50 of the mold members grip the centerpart of the plaque 40 firmly and depress it into the general cup-shapedform shown in Figures 4 and 6 and hold it in this shape while theleather take a permanent set and the elastomeric surface coatings arebeing vulcanized. The mold is closed under sufficient pressure tocompress the leather from 2030% and so held for one minute while themolds are maintained at a temperature of approximately 275 F. It will,of course, be appreciated that the pressure, molding period andtemperature may be varied over a considerable range as found to give thebest results for the particular leather and coating composition beingused. Molding may be carried out for longer periods (up to seconds) atlower temperatures, and shorter periods (down to 10 seconds) at highertemperatures, but temperatures higher than 325 F. should be avoided,else damage to the leather may result.

Slight curing of the coating opposite the cavities 47, 47 of the moldmembers may occur from the limited amount of heat reaching this area ofthe coating composition. The mold is held closed for such a shortinterval that any curing which takes place will not interfere with thesubsequent molding of a smaller sized sealing element from the discardedcentral portion ofthe plaque 40. This will behest understood by thereference to Figure 6 showing theplaque 40' afterit has been removedfromthe mold. The next stepisto' trim out thering of leather desired for thesealing member. This is accomplished by placing the seal in a trimminglathe and cutting away the unvulcan ized center along the conicalsurface indicated by a dotted line 50. The outer rim is likewise trimmedat an angle such as that indicated by a dotted line 51. The narrowflanged ringso produced forms the sealing element of the completed seal.

The salvaged central portion 48 of the disk may be. used to formradial-washer type seals or another cup-shaped sealingelement of thesame general shape shown in Figure 2 but of smaller diameter. Hence, itwill be selfevidentthat this molding technique avoids waste and permitsmaximum usage of a given plaque of leather.

We claim:

1. A shaft seal, comprising a housing ring adapted to be pressed into afluid-tight fit with a housing bore; and an annular flexible sealingring formed from sheet-leather stock, having a pair of side faces and anouter peripheral portion anchored to said housing ring with at least aportion of one face to contactthe shaft, and an inner peripheral portionslightly smaller in diameter than that of the shaft for which said sealis designed, said face of said sealing ring being sealed by a thinhomogeneous layer formed principally of oil-resistant synthetic rubbervulcanized to the immediate juxtaposed surface region only of saidsealing ring thereby leaving the body portion of said leather ringunobstructed by rubber stock and free for the capillary flow and stowageof lubricant.

2. In a metal-encased shaft seal of the type having a metal shelladapted to be pressed into a housing bore and to form a fluid-tightnon-rotating connection therewith anda flexible sealing ring of leatherhaving its outer rim anchored to said shell, said ring being shaped andarranged so that one corner of its inner rim is adapted to contact andform a running seal with a rotating shaft; that improvement whichcomprises a thin fluid-tight layer of flexible synthetic elastomerresistant to attack by lubricating mediums and impregnated with a drynon-soluble lubricant, said layer being bonded to that surface of saidleather ring adapted to have contact with the shaft, said layer beingconfined to the area of the ring immediately adjacent the surface towhich it is bonded.

3. In a metal-encased shaft seal of the type having a metal shelladapted to be pressed into a housing bore and to form a fluid-tightnon-rotating connection there with and a flexible pre-formed sealingring of leather ha ing its outerrim anchored to said shell, one cornerof the inner rim of said ring being adapted to contact andform a runningseal with a rotating shaft; that improvement which comprises a thinlayer of oil-resistant elastomer having graphite dispersed therein, saidelastomer being bonded to that surface of said leather ring in which thesaid corner of the rim is disposed and eflective to prevent the loss oflubricant by seepage from the surface of the ring to which said layer isbonded, said layer being confined to the area of the ring immediatelyadjacent the surface to which it is bonded.

4. A metal-encased shaft seal for providing a fluid-tight seal betweenstationary and relatively rotating members comprising: a rigid mountingring adapted to have a press fit with one of said members and a leathersealing ring anchored to said mounting ring at one rim, a portion of oneface near the other rim of said leather ring being adapted to pressagainst the other of said relatively rotating members and forming aruning fluid seal therewith, said seal being characterized by theprovision of a thin flexible low-friction surface-sealing layer ofoil-resistant elastomer bonded to at least the said one face of saidleather ring to prevent the seepage of lubricant therefrom withoutsubstantially interfering with the flexibility of the leather ringv orthelstowageuor. the 'flow therewithin .of

. 8 lubricant incontact with areasof said ring free of saidsealinglayer. i i T 5. In a metal-encased shaft seal for providing afluidtight seal between stationary and relatively rotating members andhaving a rigid'mounting ring adapted to have a press fit with one ofsaid members, a leather sealing ring adapted to be anchored to saidmounting ring at one rim, the other rim of said leather ring beingadapted to press against the other of said relatively rotating membersand form a running fluid seal therewith, said leather ring beingcharacterized by theprovision of a .thin flexible low-friction sealinglayer of oil-resistant synthetic rubber bonded to the hair side thereofand adapted to contact the shaft when installed in an operatingenvironment, said layer being effective to prevent the..escape oflubricant through the exterior hair side of said leather ring withoutsubstantially interfering with the flexibility of the leather ring orthe stowage or flow therewithin of lubricant in contact with areas 'ofsaid 'r'ing'having no sealing layer bonded thereto.

6. A metal-encased shaft seal for providing a fluid-tight seal betweenstationary and relatively rotating members comprising; a rigid mountingring adapted to have a press fit with one of said members, a leathersealing ring anchored to said mounting ring at one rim, the other rim ofsaid leather ring having an axially extending lip adapted to lie againstthe other of said relatively rotating members and form a running fluidseal with the surface thereof, and garter spring means for holding saidlip in contact with said relatively rotating member, said seal beingcharacterized by the provision on its exterior hair side with a thinflexible low-friction sealing layer between about 2 and 5 mils thick ofoil-resistant elastomeric materialimpregnated with dry lubricant, saidlayer being confined substantially to and intimately bonded to thesurface layer on the hair side of the leather ring to contact the shaft,whereby the remainder of the ring is free to absorb and store lubricantwhile safeguarding against loss of lubricant by seepage through the hairside thereof.

7. An improvement in shaft seals of the type having a heat moldedleather sealing ring encased in a rigid mounting case adapted to bepressed into a mounting bore surrounding a shaft; said improvementcomprising a flexible oil barrier coating between 2 and 5 mils thickbonded to the surface area only of said leather on at least the side ofsaid leather ring intended to face outwardly and to contact the shaft,said coating including as principal constituents a dry lubricantdispersed in an oil-resistant elastomer. 5

8. The improvement of claim 7 wherein said dry lubricant is chosen fromthe group consisting of graphite, molybdenum disulfide, talc, and mica,and wherein said elastomer is chosen from the group consisting of thepolymers of chloroprene, nitrile, chlorosulfonated polyethylene, andacrylonitrile-butyl acrylate.

References Cited in the file of this patent UNITED STATES PATENTS170,000 Weber et al Nov. 16, 1875 549,419 Wright Nov. 5, 1895 1,459,509Knothe June 19, 1923 1,777,984 Quimby Oct. 7, 1930 2,114,908 PetersonApr. 19, 1938 2,146,677 Johnson Feb. 7, 1939 2,248,761 7 Kosatka July 8,1941 2,647,840 Oehler Aug. 4, 1953 2,700,623 Hall Jan. 25, 1955 FOREIGNPATENTS 526,552 Great Britain Sept. 20, 1940 OTHER REFERENCES 'WhichShaft Seal? (Rainey), published in Product Engineering, May 1950,page144 (copy in 288-3) (Div.

